The bulk of our diapers have lasted through all four of our children, while they have gotten thinner over the years, which is it be expected, they have held up remarkably well. In terms of storage between children, since I was such an efficient baby-making machine (with the help of my husband, of course), the diapers never went more than a six months unused between children (thanks to infant pottying, we never had more than one child in diapers at a time!).
If you're going to be storing your diapers longterm (months or years!), there are ways to minimize potential damage from storage (mold, mildew, brittle elastic, or insect damage). If you put your diapers into storage in great shape, you will increase the likelihood that they come out of storage in great shape:
- strip your diapers before storing them to remove any lingering residues that may cause damage when they're in storage.
- sun your diapers to remove existing stains.
- clean the velcro of any lingering lint and hair
In terms of actually storing the diapers, you should keep them in a dark, dry, clean, well-ventilated area. Avoid storing them anywhere they will be exposed to extreme temperatures (like in a garage or an attic), extreme temperatures can damage textiles. If your diapers will be stored for a long time (years, as opposed to months), avoid storing them in plastic containers, which will not allow air to circulate.
If you use wool diaper covers, you will want to take extra care to avoid moth damage when they're in storage. First and foremost, clean your wool before storing it -- dirty wool is tastier than clean wool! Do not lanolize your wool cover before storing it, the lanolin can harden with time; instead, lanolize the wool after it comes out of storage. In terms of storing your wool covers, it's a good idea to enclose them in cotton (like a pillowcase, for example), with sachets of lavender, a natural moth repellent. Avoid storing your wool covers with mothballs, which can be fatal if eaten (what can I say, kids eat weird things!).
While they're in storage, it's a good idea to periodically inspect (and clean, if necessary) the storage area and your diapers. Your cloth diapers are an investment, be good to them, and they'll be good to you!